The present invention relates to an automatic transmission.
Recently, an automatic transmission (multi-speed automatic transmission) that is installed in a vehicle is required to have a plurality of speeds, such as eight forward speeds, for example. In order to facilitate easy installation to a vehicle, there is a demand for a layout in which many components, e.g., clutches, are arranged in a compact manner.
There exists an automatic transmission that includes two clutches in which either the input or output member is provided as a common member, and the other is provided as a separate member. The clutches are arranged at different positions with respect to the radial direction such that they overlap in the axial direction, thereby achieving a compact automatic transmission, particularly achieving downsizing in the axial direction (see, for example, Japanese Unexamined Patent Application Publication No. 7-269665). The aforementioned two clutches include multi-plate friction members, hydraulic oil chambers that operate the friction plates, and cancel oil chambers that cancel the centrifugal oil pressure of thehydraulic oil chambers, such that they overlap in the axial direction.
The aforementioned two hydraulic oil chambers and cancel oil chambers are arranged in a clutch drum provided as a single unit with a turbine shaft. An oil passage is formed on a boss portion of the clutch drum, and oil pressure is supplied to the two hydraulic oil chambers via the oil passage. Furthermore, of the two cancel oil chambers, the cancel oil chamber provided on the radially inner side is structured such that the oil is directly supplied via an oil hole formed in the boss portion of the clutch drum. On the other hand, the cancel oil chamber provided on the radially outer side is structured such that the oil in the cancel oil chamber on the radially inner side is supplied via an oil passage provided to the piston of the clutch on the radially inner side and via an oil passage formed in the clutch drum on the radially inner side which is a fixed member.
This arrangement allows the cancel oil chamber provided on the radially outer side to operate so as to sufficiently balance the centrifugal oil pressure that occurs in the hydraulic oil chamber provided on the radially outer side, by setting the base point of the centrifugal oil pressure further on an inner side than the radially inner side of the cancel oil chamber provided on the radially inner side. Furthermore, in order to prevent oil leakage from the radially inner side of a cancel plate (partition wall) of the cancel oil chamber on the radially outer side, an O-ring is provided on the outer peripheral surface of the clutch drum on the radially inner side that supports the cancel plate.